Preparation and characterization of several transition metal oxide systems

Tetragonal ZrO2 is prepared by decomposing either the basic carbonate or the basic nitrate. The oxide obtained from decomposition of the carbonate shows a higher surface area and smaller crystallite size. Transformation of the tetragonal to the monoclinic phase is studied as a function of temperature, and a pattern fitting technique is used to analyze the phase fraction. Samples of stabilized cubic ZrO2 are prepared containing Rh(III) and La(III). The properties of these compounds are studied by X-ray and thermogravimetric analyses. The cubic phase becomes stabilized with the incorporation of La(III) and Rh(III), and Rh(III) in the ZrO2 becomes stabilized towards reduction. Samples of Cr2-xRhxO3, Co3-xCrxO4, CrxFe2-xO3, and NiO/NiCr2O4 are prepared by decomposition of the nitrates. The reducibility of these compounds are studied by temperature programmed reduction studies. Rh(III), Fe(III), Ni(II), Co(III) and Co(II) in these compounds becomes stabilized towards reduction. Cr2O3 reduces to Cr at lower temperature with the presence of Rh, Fe, Co, or Ni. The superconducting oxides La1.8Sr0.2Cu4 and YBa2Cu3O7 are prepared and thermogravimetric analysis indicates the presence of Cu(I) and Cu(III) in La1.8Sr0.2CuO4. The compound YBa2Cu3O7 prepared from nitrates and annealed in oxygen at 425 degree C gives a sharp superconducting transition at 92 K. The phase is stoichiometric but decomposes when kept in contact with moist air